Round balers generally have a bale forming chamber defined by a periphery apron comprising an array of side-by-side belts, transverse slats trained on chains, a plurality of rolls or a combination of these various elements, e.g. rolls and belts. Crop material such as hay or straw or another crop is picked up from the ground as the baler traverses the field and fed into a fixed or variable chamber where it is accumulated and compressed to form a cylindrical package of crop material. The formed package, while in its compacted condition inside the chamber, is wrapped with net, plastic film, twine or the like, to produce a completed round bale which is then ejected from the chamber onto the ground for subsequent handling.
The device for wrapping net or plastic film around the crop material in the baling chamber commonly comprises a supply roll of wrapping material, a mechanism for dispensing wrapping material from the supply roll to the baling chamber and a cutting mechanism for severing the wrapping material after a suitable length has been wound about the bale.
In order to preclude uncontrolled unwinding of the net or film from the roll in between wrapping operations, a brake mechanism is mounted to the supply roll. The brake mechanism can also be used to tension the wrapping material between the supply roll and the baling chamber during the actual wrapping operation.
In DE-U-84.01.166, the supply roll rests on the bottom of a supply container and braking action is provided by the friction of the roll against the bottom and wall of the supply container. However, the friction force is largely dependent on the properties of the container surface and the wrapping material on the one hand, and on the diminishing weight of the roll on the other hand. Hence, the resulting force on the dispensed net is subject to large variations.
The wrapping device shown in U.S. Pat. No. 5,448,873 comprises a roll which is supported on a transverse shaft and a brake element which is in state of rest biased by a spring against the periphery of the roll. Once again, the friction forces here are largely dependent on the surface properties of the wrapping material. Furthermore, the stretching forces tend to diminish as the diameter of the roll decreases and the bias spring is relaxed.
EP 0 807 380 of the applicant overcomes the disadvantages of these earlier proposals and is believed to represent the closest prior art to the present invention. The wrapping device of this patent comprises a supply roll supported on a transverse support shaft mounted for rotation between the side walls of the main frame. An device, constructed as a so-called duckbill, receives wrapping material from the supply roll and feeds it to the periphery of a completed bale package at the commencement of a wrapping operation. A cutter severs the wrapping material after a suitable length has been wrapped about the periphery of the bale.
In order to maintain a desired tension in the net or wrapping material as it is being unwound from the supply roll, a brake drum is engaged by a brake shoe secured for rotation with the support shaft. An improvement taught by EP 0807380 is to vary the force by which said brake shoe is pressed against the brake drum in dependence upon the amount of wrapping material remaining on the supply roll.
The operation of the wrapping device of EP 0 807 380 will now be described with reference to the accompanying FIGS. 1, 2 and 3 which correspond to FIGS. 4, 5 and 6 of the latter patent, respectively. These drawings show side views of the wrapping device at three different stages in the operating cycle. The drawings will be described below only to the extent necessary for an understanding of the present invention. They are however described in greater detail in the specification of EP 0 807 380, which, in the interest of brevity, is incorporated herein by reference in its entirety.
In FIGS. 1 to 3, only part of the baling chamber 10 can be seen in the drawings and it is located to the right of drawings. The wrapping material 12 is wound on a supply roll 14 and the braking mechanism 16 acts on the supply roll 14 to control the web tension while the bale is being wrapped. In the drawings, the braking mechanism 16 is shown in solid lines whereas the parts of the baler not associated with the braking mechanism are shown in broken lines.
FIGS. 1 and 2 show the wrapping mechanism as a bale is being wound. A supply roll 14 is mounted on a transverse support shaft 15, rotatably supported between the side walls of the main frame of the round baler. Wrapping material 12 drawn from the supply roll 14 passes through a duckbill 18 and cutter 20 into the baling chamber 10. The correct tension in the wrapping material 12 is maintained by controlling the braking of the supply roll by the braking mechanism 16, which will now be described in greater detail.
The braking mechanism 16 comprises a brake shoe 22 fitted to a lever 24 biased counter-clockwise by a spring 26 to make contact with a brake drum 23 that is connected with the supply roll, for example via the transverse support shaft 15 for the supply roll 14. A separate actuating lever 28 pivoted about the fulcrum of the lever 24 is biased in state of rest by a spring 30 to increase the braking force. The opposite end of the spring 30 is anchored to a lever 32 connected to a follower 34 with a follower roller 35 such that its position varies with the diameter of the supply roll 14. This can readily be seen from a comparison of FIGS. 1 and 2. In this way, as the supply roll 14 diameter reduces, so does the force applied by the spring 30 and the braking force applied by the brake shoe 22. Consequently, the tension on the wrapping material 12 remains under substantially the same tension as the wrapping material 12 is unwound form the supply roll 14 and its diameter reduces.
A manually operated lever 40 is provided for rotating the lever 24 clockwise to release the brake entirely when the supply roll 14 is to be changed.
Once the desired length of wrapping material 12 has been wound about the formed bale, it is cut using the cutter 20. Following this, the formed bale is discharged from the baling chamber 10 and more crop is introduced into the baling chamber to create a fresh bale.
Once the baling chamber 10 is full, a signal from a suitable sensor is generated to commence a wrapping operation. E.g. the signal is used by a controller of the baler to operate a hydraulic actuator 50 which is connected to the duckbill 18 to advance it from a state of rest that corresponds approximately with the position shown in FIG. 1 or 2 to a position that corresponds approximately with the position shown in FIG. 3 that is to say towards an opening in the baling chamber 10 where the web is picked up by a stripper roller 52 and pressed against the outer surface of the bale. The duckbill 18 is also connected by a rod 54 to the brake actuating lever 28 such that by the time that the wrapping material 12 is engaged by the stripper roller 52 and dragged into the baling chamber 10, the braking force will have been released to allow free movement of the wrapping material 12. The duckbill 18 then retracts over a certain distance to the position shown in FIGS. 1 and 2, so that the braking mechanism 16 exerts a braking force to maintain the desired tension in the wrapping material 12. The duckbill 18 subsequently returns completely to its state of rest whilst the braking mechanism 16 continues to brake and the cutter 20 cuts the wrapping material 12 between the supply roll 14 and the baling chamber 10.
A problem is encountered with the wrapping mechanism of EP 0 807 380 if the wrapping material 12 is dragged into the baling chamber by the stripper roll 52 before the duckbill 18 has reached the position in which the braking mechanism 16 is sufficiently released. The distance between the end of the duck bill 18 and the cutter 20 in FIGS. 1 and 2 is, say, about 10 cm and, as a result, a flap wrapping material 12 of this length is assumed to protrude from the end of the duckbill 18 at the commencement of the wrapping operation. However, under certain circumstances, such as when the supply roll 14 is replaced by a new the supply roll 14 with wrapping material 12 with different properties or when wrapping material is irregularly cut as a result of wear and tear in the cutting installation or local quality problems in the wrapping material, the length of the flap of wrapping material 12 projecting from the end of the duckbill 18 may change to, say, 20 cm or more, or long tatters may form of 20 cm or more for example. In such cases, the wrapping material 12 will be gripped by the stripper roll 52 whilst the braking mechanism 16 is still applied and this results in tearing of the wrapping material.